Process of making iron-aluminum alloys and components thereof



Jan. 18, 1966 A. ROY ETAL 3,230,074

ALUMINUM ALLOYS .AND COMPONENTS THEREOF 3 Sheets-Sheet l A. ROY ETALJan. 18, 1966 3 Sheets-Sheet 2 Filed July 16, 1962 R E m um Ww, y @YAM Mm WOM, W o 155. o. ...n.0 d M L X .1W www. m M U FL W Maw 5f LU 0% CR uRMNWRNWJ .UNNMKAGN HW d@ @a M M m, M Y w.. nu a & f 1m m m. d a M W M w0 Z .rmrmxQ J 5. 4 f a 7 L/ f, w, w M .mm RS $12k Jan. 18, 1966 A. ROYETAL 3,230,074

PROCESS OF MAKING IRON-ALUMINUM ALLOYS AND COMPONENTS THEREOF Filed July16, 1962 3 Sheets-Sheet 5 mvENToRs A M DE a Ro Y CLAUDE BELLE/4U RUSSELLD. SPENCER United States Patent 3,230,074 PRUCESS GF MAKINGIRON-ALUMINUM ALLOYS AND CGMPONENTS THEREF Amedee Roy, Ferndale, ClaudeBelleau, Troy, and Russell D. Spencer, Warrem Mich., assignors toChrysler Corporation, Highland Park, Mich., a corporation of DelawareFiled July 16, 1962, Ser. No. 209,939 14 Claims. (Cl. 7S-49) Thisinvention relates to ductile iron-aluminum alloys and especially to aprocess for making the same. It is also concerned with novel proceduresfor reducing the carbon content of the carbon-containing iron (generallycalled a steel) base ingredient for such iron-aluminum alloys.

In the pending application Serial No. 655,191 of applicant Amedee Royand one Walter E. Iominy, tiled April 26, 1957, no-w U.S. Patent No.3,059,326, granted October 23, 1962, it is set lforth that the coldworking of iron-aluminum alloys (usually requiring at least about and inmany cases 20% elongation on standard tensile testing specimens at roomtemperature) is adversely atiected by carbon additions or inclusionsabove about 0.03% to 0.05% by weight.

Moreover, it is indicated that iron-aluminum alloys having in excess ofsuch carbon and containing 10% and more aluminum lack sutlicientelongation (have less than about 5% elongation) `for room temperaturefabrication, and are brittle. It is also there indicated that attemptsto reduce room temperature brittleness by the use of vacuum duringconventional melting of the iron and aluminum resulted in someimprovement in the hot rolling characteristics of the material and thatwhere in such operations hydrogen was passed through the melt or carbonadditions made thereto to produce this result, some further improvementin -ductility was feasible. These improvements are, however, costly toelect and do not produce optimum ductility characteristics.

The present invention is directed to a new, and novel, process forproducing iron-aluminum alloys of substantial uniformity and ductilitycharacteristics, capable of being cold or hot worked and to the alloysper se having these properties.

An object of the invention is to provide a process involving iirstproviding a carbon-containing iron melt capable of combination withsubstantially pure aluminum to form `a ductile iron-aluminum alloy and.then adding to and mixing with the molten iron a predetermined amountof such aluminum.

A particular object is to provide a process of making ductileiron-aluminum alloys wherein aluminum in solid form is added to molteniron containing less than 0.03% carbon by weight.

Another particular object is to provide a process for reducing thecarbon content of a body of iron containing in excess og 0.03% carbon-by weight, which iron is to be alloyed `for producing a ductileiron-aluminum alloy comprising melting a body of said iron, transformingsaid body of molten iron into a moving stream thereof, dispersing saidstream and subjecting said dispersed stream `to vacuum to remove oxidesof carbon therefrom.

A further object is to provide a process as in the preceding objectwherein the body of iron is made to contain sufficient oxygen for thecritical oxygen equilibrium requirement for the amount of carbon in themelt.

Another object is to provide a process of making irona-luminum alloysinvolving the treatment of an iron melt to reduce its carbon content toWithin sta-ted critical limits, and to thereafter add to the molten ironin predetermined amount substantially pure aluminum in solid form, andin a manner yto effect its uniform distribution in the melt to providean ultimate ductile iron-aluminum alloy.

An additional object is to provide a process of producing ductileiron-aluminum lalloys as in the preceding object, wherein the reductionin caubon is effected by vacuum degassing of a molten stream of steel towhich critical amounts of aluminum are subsequently added while thelatter is still molten.

Another object is to provide a process of producing ductileiron-aluminum alloys involving treating a steel melt under vacuumconditions to reduce the carbon content to below about 0.03% by weight,and thereafter adding substantially pure aluminum in solid form inamount between about 3 to 12% by Weight to` produce a ductileiron-aluminum alloy, said steel melt con-taining or having added theretoduring processing sutiicient soluble oxygen according to the equilibriumrequirements of the initial carbon content of the melt for effectingsaid carbon reduction.

A further object is to provide a processes in the preceding objectwherein the steel melt initially contains carbon in amount less thanabout 0.2% by weight.

Still another object is to provide a procedure `for reducing to belowabout 0.03% the canbon content of a molten steel containing or to whichsoluble oxygen has been added, comprising directing the molten steelthrough a restricted orice into a chamber subjected to vacuum to producea particle stream thereof, wherein the soluble oxygen combines withsoluble carbon to form carbon monoxide and some carbon dioxide gas, andsubjecting the stream to a vacuum suliicient to remove these gases fromthe stream.

A further object is to provide a method of producing ductileiron-aluminum alloys from ingredients including a high carbon-containingsteel which comprises initially melting and treating the steel under aprotective blanket of slag or gas and at atmospheric pressure to etect aboil of the melt to reduce the car-bon content thereof; then forming themolten steel into a fan-like stream, and subjecting the stream to vacuumdegassing to `further reduce the carbon content and then adding aluminumin predetermined amount, in solid fontn, to the thus treated steel, andunder conditions inhibiting volatilization of the aluminum.

A specific object is to provide a process comprising melting a body ofiron by induction heating while subjecting said body of iron to vacuum,after melting said iron, separately heating a solid mass of aluminum -byinduction heating and combining said molten iron with said aluminum intoa uniform mixture while continuing the application ot' said vacuum.

Other objects and advantages of the invention will appear from theyfollowing `description and from Ithe drawings, wherein:

FIGURE 1 is a schematic sectional view in elevation showing a form ofapparatus by which the present invention may be performed;

FIGURE 2 is a graph showing the relationship between carbon and oxygencontents in iron at 2800 F1 at various pressures;

FlGURE 3 is a graph showing the effect of carbon on certain physicalproperties of a wrought iron-aluminum alloy containing 6% aluminumannealed for one hour at 1500o F. and air cooled;

FIGURE 4 is a graph showing the Fe-Al-C diagram for an iron-aluminumalloy containing 6% aluminum; and

FIGURES 5 and 6 are schematic sectional views of additional forms ofapparatus .by which features of the present invention may be obtained.

The invention is based upon a number of considerations, in parttheoretical and in part derived by experimentation. For example, it isfounded rst, on the recognition that the carbon content Of a steel meltis susceptible to reduction by combining it with other elements to formmetallic compounds upon cooling, and that when soluble oxygen is presentin the melt it may, under proper conditions, interreact with carbon toproduce a removable gaseous oxide such as carbon monoxide (CO) and somecarbon dioxide (CO2); secondly, upon the fact that the extent to whichthe latter is possible is dependent upon there being sufficient solubleoxygen in the melt, and preferably an amount equal to or exceeding thecritical oxygen equilibrium condition for the amount of carbon presentin the melt; thirdly, upon the finding that substantial dispersing orparticulating of the melt occurs when a moving uid body thereof ispermitted to impinge upon a bulbous protuberance or to be released as astream into a low pressure medium from one where it is subjected toatmospheric or higher pressure, which dispersing and/or particulating isconducive to the formation of carbon monoxide and some carbon dioxide bythe soluble ycarbon and oxygen of the melt and that the simultaneousapplication of suicient vacuum under these conditions also facilitatesthis formation of gaseous oxides and furthermore facilitates theirexpeditious removal from the melt; and fourthly, upon the finding thatfor optimum alloying, the aluminum additions should be made t-o the ironmelt in :solid (i.e., unmelted) form after the iron melt has beenconditioned for allowable critical carbon content and preferably in amanner to avoid exothermic reactions and volatilization of the aluminum.

Although iron-aluminum alloys having the desired room temper-aturefabricability may be produced using for the iron component highlypurified electrolytic iron, such is very costly and unpracticable wherelarge quantities are involved. Therefore other commercial steels must beutilized. These normally contain substantial amount-s of carbon whichmust be reduced prior to making the aluminum addition. We havediscovered that it is possible to initiate processing with a steel stockcontaining a relatively high amount, for instance about 0.2% by weightand more of carbon and which may be scrap steel, or by startingprocessing with steel stock containing a relatively low amount, forinstance about 0.1 to 0.2% by weight and less carbon.

If, for example, the charge contains carbon in the high range, forinstance 0.6 to 1.0% carbon, as in the case of commercial steel scrap,it will first be treated by conventional melt procedure to reduce thecarbon content to a minimum possible in this maner, and thereafter bythe vacuum procedures described above to further reduce the carboncontent. Thus considering the use of steel scrap and `in a large batchthe charge is first preferably melted in a suitable furnace atatmospheric pressure, preferably in a furnace chamber or Crucible linedwith magnesium oxide or other refractory, `and with the melt under ablanket of slag (preferably composed of limestone, fluospar, andcryolite) or argon gas, and at a temperature sufficiently high, forexample between 2800 and 3l00 F,. during which any readily combinablesoluble carbon and oxygen may react to form carbon monoxide or carbondioxide and cause an active boil tending to stir the melt into activemovement and facilitate escape of the gaseous oxide of carbon throughthe blanket. Heating the melt `for about one hour more or less dependingupon melt conditions and the size of the melt will usually suffice.

In order to effect optimum reduction in the carbon content of the steelby this procedure, it is usually desirable to lance the melt with oxygenby blowing oxygen into the melt or by adding oxygen-containing compoundssuch as iron oxide to provide oxygen to the melt.

The carbon reduction by this process is seldom to a level below about0.03% and always insufficient for directly utilizing the same in themaking of a substantial ductile iron-aluminum alloy such as describedabove. Accordingly, further treatment of the melt is required. This mayfor example be carried out in an apparatus such as shown in FIGURE lwhere the fluid charge 9 of the above initial processing has beentransferred while 4 still molten to a ladle 10. The ladle 10 of FIGURE 1is preferably lined at 12 with magnesium oxide refractory material andhas a bottom bell mouth nozzle-like pouring outlet 14 through which astream of the molten iron may flow and which may be manually closed by asuitable rod stopper 16. No protective blanket is required in thetransfer operation, and it and the steps hereinafter described arerelatively promptly performed to avoid extraneous heating. It will beunderstood that heating may be provided if desired.

From the ladle 10 the fluid melt is discharged under atmospheric orhigher pressure through the bottom pouring outlet 14 into a smallintermediate chamber or cavity 18 provided in a housing 20 secured inthe roof or cover 22 of a vacuum chamber 24 defined by a casing 26 andsaid cover 22. The cavity 18 has a converging nozzletype dischargeoutlet 28 at the bottom thereof from which the melt is discharged intoan open-top ladle 32, also preferably lined with magnesium oxiderefractory material as at 34. The ladle 32 is suitably supported onpivotal trunnions 36 within chamber 24. The chamber 24 into which themelt is directed is subjected through an opening 38, by conventionalmeans not shown, to a vacuum as great as practicable; for examplecorresponding to a pressure of less than about 0.1 atmosphere. As themelt is released into the vacuum chamber the differential pressure or,stated otherwise, the sudden release of pressure, causes it to bedispersed, automatically fan out and become in effect a stream 40 ofmany individual droplets or particles of molten metal.

It is found that by this action it is possible to facilitate interactionof the soluble carbon and oxygen remaining in the melt to an extent nototherwise possible. By preference, he dispersed stream 40 of moltenmetal will be made to travel over a substantial distance, preferably inthe order of several feet, since such will further facilitate thereaction between any soluble carbon and oxygen carried in the stream toform gaseous carbon monoxide which will bubble from the stream or bepumped out of the stream by the vacuum applied at 38 and removed fromthe chamber. It has been found possible by the described step to reducethe carbon of the melt received in the ladle 32 from an amount, forexample 0.03% by weight to below 0.002% by weight, depending upon thedegree of vacuum employed and the suiciency of the oxygen in the melt.

The addition of aluminum to the molten iron may be made by injecting itinto the molten dispersed stream where it discharges into the melt inthe ladle 32 or to an accumulation thereof in the ladle. It may also bemade while vacuum still exists in the chamber 24 or while it issubjected to above atmospheric pressure or after removing the ladle fromthe vacuum chamber.

It is preferred to add the aluminum under a layer of molten iron andwhile the aluminum, preferably preheated, is in a solid state. Thelatter is desirable to avoid a high rate of volatilization of thealuminum, which can occur where molten aluminum is added, and atemperature rise by exothermic reaction.

The aluminum addition in amount between about 3% to 12% by weight andpreferably between Bil/2% to 8% but in any case not more than willproduce a ductile ironaluminizing alloy capable of room temperaturefabricability may be made, for example through a hopper 42 having adischarge outlet 44 arranged over the mouth of the ladle 32 andcontrolled to feed or inject predetermined quantities of aluminumpellets or granules 46 into the stream 40 or to an accumulation in theladle 32, in accordance with the rate of discharge of iron melt from thedischarge nozzle 28. Aluminum pig may also be placed in the ladle 32prior to commencing discharge of the melt thereto, the impingement ofthe stream 40 aiding in keeping the metals mixed. The use of aluminumwire or rod which can be fed through the means 42 into the ladle 32under the surface of the melt and at a constant rate is alsocontemplated.

It will be understood that where the steel melt initially contains 0.1%carbon or less, the preliminary treatment of the melt may be omitted andthe melt directly subjected to the vacuum stream treatment described.

Instead of using the apparatus of FIGURE 1, for the further removal ofcarbon from the iron component, the iron melt after the initial carbonboil treatment described above may in any known manner be transferred inmolten form to the melting ladle 50 of an induction furnace 52 shown inFIGURES 15 and 6 having a current carrying coil S4, and suitablysuported as on a pivotal trunnion 56 in chamber 57 of a housing 58 towhich a vacuum such as described with respect to FIGURE 1 is appliedthrough the opening 60. It will be understood that if desired the chargeof iron scrap may, if not excessive, be initially melted in the furnace52 and subjected to carbon boil by vacuum to reduce the carbon content.

In either event the molten iron is then either poured into a ceramicmold or receptacle 62 as in FIGURE 5 or into a further induction heatedladle Crucible or receptacle 64 as in FIGURE 6.

The receptacle 62 as seen has a central bulbous protuberance 66 definingwith the side and bottom walls 68, 7i) of the mold a ring-likedepression or well 72 into which the molten iron may ow and accumulate.As the poured stream 74 of iron from the ladle 50 strikes theprotuberance 66 it is dispersed into a fan-like stream of particles ordroplets of molten iron such as in case of the stream 40 in FIGURE 1facilitating the combining of soluble carbon and oxygen into gaseouscarbon monoxide and some carbon dioxide which is thereupon removed fromthe stream by the vacuum action thereon in the chamber 57. Since theprotuberance 66 forms part of the mold bottom it will be recognized thatdispersement of the stream 74 by the same is limited by the extent oiits projection above the base 70.

This condition is overcome by the arrangement in FGURE 6 where the ladleor Crucible 64 of the induction heated furnace 76 having a currentcarrying coil 7S, is provided with a bottom bell-mouthed pouring outlet80 closed by a manually or power operable stopper means generallydesignated by the numeral 82.

As seen the stopper means 82 comprises a hollow stem S4 having a closedstopper and member S6 and a bulbous head 8S which serves to disperse thestream 74 as in the case of the protuberance 66, of FIGURE 5. Thestopper means S2 may if desired be liquid cooled by any suitable means.It will be noted that in the FIGURE 6 arrangement the molten iron mayaccumulate for a considerable depth in the Crucible 64 withoutinterference with the action of the head S8. The stopper means 82 may beoperated in any suitable manner by the bent rod 90 having an extension92 in the plane of the drawing which may be fulcrumed in a cover member94 of the housing 53 and pass through the same so as to be operableexternally of the chamber 57 for raising or lowering the stopper means82.

The housing 5S may include a lower section 1100 providing a chamber 102which is optionally provided with vacuum in which a mold or receptacle104 may be positioned to receive the molten metal from the crucible 64.

Obviously aluminum additions may be made to the molten iron in thereceptacles 62, 64 in the manner described above. The arrangement inFIGURE 6 is particularly adaptable for this function since solid pelletsor bars of aluminum may be placed in the Crucible 64 without subjectingthem to a temperature above the melting point While the iron is beingmelted and/or treated in the ladle 50 of the separate induction heatedfurnace 52. This is possible because the furnaces 52, 76 are separatelycontrollable. Manifestly the temperature of the furnace 76 may be raisedif desired after pouring of the metal from the ladle 50 has started. Itwill also be evi- 6 dent that once the Crucible 64 is filled to thelevel of the head 88 the head may also serve to keep any bars ofaluminum placed therein submerged in the iron until melted. lFurthermorethe induction heating acts to keep the molten iron in motion to assuregood mixing of the aluminum therewith.

The thermodynamic considerations concerned with the equilibrium ofcarbon and oxygen in a molten iron bath have heretofore :beeninvestigated by others. The controlling reaction representing theequilibrium of carbon and oxygen is given by the equation:

Moreover, the equilibrium constant K of the above reaction in the lowconcentration ranges of carbon and oxygen is attained by experimentaldata reported by Chipman et al. in the Transactions of the A.S.M. 1941and is expressed as follows in a relationship lof the partial pressureof CO and the percentage concentration of both `C and O in the melt:

Referring to FIGURE 2, the graphs there shown are based upon the abovethermodynamic considerations and curve C is plotted using onlyexperimental data. These curves provide a means `of determining withreasonable .accuracy the sufciency of oxygen in a given melt forequilibrium conditions and the reduction in carbon content of a meltpossible from a given level thereof by the use of the proceduresdescribed above involving the formation and removal of CO from the melt.

Thus the curves in FIGURE 2 show the relationship between carbon andoxygen contents at 2800 F. at varous pressures. Curves A, B and D arebased on .theoretlcal calculations and curve C upon actual experimentaldata. Curve A shows the relative concentration of oxygen .and carbon inequilibrium in an iron-rich bath at one atmosphere of pressure. Curve Bshows the reduction in concentration of oxygen and carbon inequili-brium when the bath is exposed to 0.1 atmosphere of pressure.Curve C shows the extent of improvement in carbon reduction possiblewhen the molten bath is exposed to a pressure ranging from 5X 10-6 to 510-2 millimeters of mercury, as obtained by experimental data, and curveD shows the results obtainable at a pressure of 0.01 atmosphere. Thevariations between curves C and D are due to thermodynamic factors.

`From these curves it will be seen, for example, that an iron meltcontaining approximately 0.045% carbon would at one atmosphere ofpressure have an equilibrium oxygen content of 0.0485 Moreover, that ifsuch melt is exposed in the manner described above to a lower pressure,for example 0.1 atmosphere, there would result as shown by curve B alower equilibrium value for C and O. The reduction in each will followthe above equation 1/2O2--C2CO; i.e., some of the soluble C and solubleO will combine in the course of treatment of the melt to produce CO atthe lower pressures. From curve D it will -be evident that anequilibrium condition can be attained at a pressure of 0.01 atmosphere,whereby the carbon content is reducible to 0.011%.

The graph in FIGURE 3 is based upon experimental test data obtained withtest bars of a wrought iron aluminum alloy lcontaining 6% by weight of`aluminum and varying amounts of carbon after a one-hour lanneal 4at1500 F. It shows the changes eifected intensile strength and elongationfor carbon contents of between 0.005% and 0.12%.

The graph in FIGURE 4 shows the Fe-Al-C diagram for iron-aluminum alloyscontaining 6% aluminum, and varying amounts -of carbon as obtained frommetallurgical samples. From this graph it will be evident that by theproper amounts of carbon it is possible to obtain alloys operable over awide range of temperature while i* maintaining a substantially whollyferritic con-dition.

The following examples are illustrative of the application of thefeatures of our invention and are not intended to place a limitati-onupon its scope.

Example 1.-A heat of about 2800 lbs. was prepare-d in lan electricfurnace in the following manner: 2500 lbs. plain carbon steel scrap4containing 0.5% carbon was partially melted and `60 lbs. of lime (CaO)was added to the partially melted steel so as to produce a good basicoxidizing slag effective to remove phosphorous and sulphur impurities.When Iall of the scrap was melted 270 lbs. -of ir-onore ('Fe203) wasadded.

The function of the iron ore was to laid in reducing the carbon contentof the bath. The melt, with its slag |blanket, was then treated withoxygen for ve minutes by blowing oxygen into the bath from a suitableexternal source through a 1/2 lance. The temperature of the bath at thistime was 2880 F. The effect of this treatment was to reduce the carboncontent of the melt to 0.03%.

The oxidizing slag blanket was then slacked olf and the bath againlanced with oxygen for three more minutes while raising its temperatureto between 2900 and 2950 F. Electrolytic manganese in amount of about 5lbs. was then added t-o the bath along with a reducing slag mixturecomposed of fresh lime, fluospar and cryolite, and granular aluminum.S-ucient slag mixture was added to cover .the bath. The slag mixture waslluxed within four minutes without the use of any electric power. Thereducing slag serves to remove ex-cess oxides and oxygen.

The reducing slag blanket was then slacked off and the heat then tappedoff into a ladle preheated to a temperature of about 1000 F. within sixminutes after the reducing slag was added to the bath.

Prior to transferring the melt to the ladle, sufficient primary (pure)aluminum in an amount of about 6.67% by weight of the melt was placed inthe ladle and preheated (but not melted) in the ladle. Also followingtapping of the heat a small amount (about 0.02%) of calcium-siliconalloy was added to the ladle and the melt stirred with a furnace testspoon to assure a uniform composition of the metal.

The melt was now teemed into a sixteen-inch round corrugated moldthrough a 21A nozzle. 'Ihe mold was clean, uncoated, and warm beforepouring. A clay hot top was placed into position on the mold withasbestos rope used at the junction to prevent any leaks. Before pouringwas started about one pound of crushed cryolite was added to the bottomof the mold. A sixteen-inch round ingot weighing 2450 lbs. was producedin this operation, plus excess scrap butt of 500 lbs.

T-he ingot was cooled in the mold to room temperature before stripping.

Example 2.--Fifteen pounds of Armco iron containing 0.012% to 0.015%carbon by weight was melted in a magnesium oxide (MgO) lined Crucible ata temperature of about 2900 F. The charge was covered with a slagblanket made up of a 50 gram l-to-l mixture of limestone (CaCO3) andiluospar (CaFz). The charge was fully melted in about 45 minutes and wasthen superheated under its slag blanket to 3000 F. to assure sufficientheat for the subsequent addition of aluminum. The melt was thendeoxidized by the addition of 0.02% calcium silicon (CaSi) alloy.Aluminum pig in amount to produce a 6% iron aluminum alloy was thenpushed in unmelted form under the blanket of slag and melted down inthis manner. The bath was then stirred with a low-carbon steel or Armcoiron rod. The temperature of the bath was then increased to 3100 F.,after which the slag blanket was removed and the melt immediately pouredinto a 21A octagonal shell mold made from a mixture of molding sand andphenolic resin binder.

The riser of the mold was covered with Sil-O-Cel refractory heatinsulating material and the mold was then permitted to cool to roomtemperature before stripping the alloy therefrom.

Example 3 For-ty-five hundred grams of cornmercial Armco iron containingabout 0.012% carbon was melted in a magnesium oxide lined Crucible undervacuum in a Stokes vacuum induction unit, as shown in FIG- URE 5.

After the charge was fully melted and was further heated by inductionfor about live minutes, a sample of the bath was taken and showed thepresence of 0.005% carbon by weight. The melt was then heated to 3100DF. and 0.30 gram of graphite added. This increased the carbon content ofthe melt to 0.021% carbon by weight. Fifteen to 20 grams of iron ore inthe form of Fe2O3 was then added to the melt to provide additionaloxygen to the melt.

The vacuum chamber was then pumped down to a vacuum of better thanmicrons of Hg (100/a) and while thus subjected to vacuum was poured as astream from the narrow pouring lip of the Crucible into a 6 diametermold 18 to 24" below the same. The mold had a central raised hump suchthat the molten metal stream could impinge thereon and splash into themold, thus breaking up the stream and facilitating the degassing action.The metal in the mold was then permitted to cool to room temperaturewhile still subjected to vacuum. A sample of the metal showed thepresence of 0.006% carbon.

Example 4.Twentytwo hundred fty grams of Armco iron was melted under ablanket of argon gas in a Stokes vacuum induction unit. After the chargewas fully melted and was further heated by induction for about liveminutes a sample of the bath was taken and 1showed the presence of0.007% carbon by weight. The melt was then heated to 3100 F. and 0.30gram of graphite added. This increased the carbon content of the melt to0.135% carbon by weight. The melt was then saturated with oxygen bylancing the same with oxygen for 30 seconds at a pressure of 10 p.s.i. Asample taken of the melt at this time showed the presence of 0.0l21%carbon.

The vacuum chamber was then pumped down to a vacuum of better than 500microns (500e) A sample taken at this time of the melt showed 0.006S%carbon. The melt, while still subjected to vacuum, was then streampoured and splashed into a mold as in Example No. 3, during whichcontinued degassing of gaseous oxides occurred. The metal was permittedto cool in the mold while under vacuum. A `nal sample showed the carboncontent to be 0.0036%.

Example 5.794.75 lbs. of Armco iron containing 0.013% carbon was meltedin an induction heating furnace using a magnesium oxide lining and undera Vacuum equivalent to a pressure of 20 microns of mercury. Thetemperature of the bath was about 2850 F. Four to 5 lbs. of mill scale(Fe203) was added to provide additional oxygen to the melt to facilitatea further reduction in the carbon content by carbon boil. The melt wasmaintained under vacuum for about 30 minutes to accomplish this result.A sample of the iron was then checked and analyzed at 0.003% carbon.

The bath was then optionally treated to deoxidize the same by theaddition of .02% CaSi, after which 55.25 lbs. of solid aluminum pig ofcommercial purity (99.9% pure) was added to the molten iron and stirredin by induction mixing. During this procedure the melt remained undervacuum. The temperature of the melt was then raised to 2950 to 3000 F.,and then poured into 3" thick 10" x 14" steel tapered molds.

In Examples 3 and 4 the addition of graphite was for the sole purpose ofraising the carbon content of the steel melt to a substantial amount orto above the critical for the ductile iron-aluminum alloy and toestablish the vacuum stream treatment as a procedure for reducing thecarbon content of the melt. Such carbon addition would not be made incommercial practice.

From the above description of our invention it will be evident that wehave provided a novel procedure for conditioning an iron or steel meltfor combining with aluminum to produce ductile iron-aluminum alloys andprocessing for making the aluminum additions. lt will be understood thatwhile stream dispersing of the steel melt while subjected to vacuum isespecially effective for reducing the carbon content thereof prior tomaking the aluminum addition that the application of vacuum to a meltalone has given good results.

It will be undersood that various changes and modifications in theabove-described procedures and apparatus will suggest themselves tothose skilled in this art without departing from the spirit and interestof our invention. All such changes and modifications coming within thescope of the appended claims and equivalents thereof are thereforecontemplated.

-We claim:

1. The process of preparing ductile iron-aluminum alloys comprisingdirecting a stream of molten iron having a carbon content above about0.03% and up to about 0.2% by weight from a source thereof to areceptacle in which said molten iron is to be collected, said molteniron containing soluble carbon and oxygen, subjecting said stream ofmolten iron to a vacuum equivalent to a pressure of less than about l/ioof an atmosphere and dispersing said stream while subject to said vacuumto reduce the ferrostatic pressure thereon and produce a stream ofdroplets of molten iron increasing the exposed area of said stream tosaid vacuum to thereby induce the formation of gaseous oxides of carbonfrom said soluble carbon and oxygen in said stream, continuing theapplication of said vacuum to remove said gaseous oxides from saidstream and reduce the carbon content of the molten iron collected insaid receptacle to an amount below 0.03% by weight, introducing solidaluminum into the receptacle in a manner such that the aluminum isbrought into contact with the substantially degassed stream of molteniron beneath the same, and introducing said aluminum in amount toproduce an iron-aluminum alloy containing between about 3 to 12% byweight of aluminum, said alloy being ductile.

2. The process of preparing ductile iron-aluminum alloys comprisingdirecting molten iron having a carbon content above about 0.03% and upto about 0.2% by weight through a restriction to form a flowing streamthereof, said molten iron containing soluble carbon and oxygen,subjecting said stream upon its discharge from said restriction to avacuum equivalent to a pressure of less than about 1A@ of an atmosphereto disintegrate the stream into molten droplets of iron and increase theexposed area of said stream to said vacuum, whereby to induce theformation of gaseous oxides of carbon from said soluble carbon andoxygen in said stream, continuing the application of said vacuum uponsaid stream to remove said gaseous oxides therefrom and reduce thecarbon content of the molten iron to an amount below 0.03% by weight,feeding solid aluminum to said stream of molten droplets or iron at thebase of said stream and at a rate in accordance with the rate ofdischarge of the molten iron from said restriction, and feeding saidaluminum in amount to produce an ironaluminum alloy containing betweenabout 3 to 12% by weight of aluminum, said alloy being ductile.

3. The process of preparing ductile iron-aluminum alloys comprisingdirecting a stream of molten iron having a carbon above about 0.03% andup to about 0.2% by weight from a source thereof to a receptacle inwhich said molten iron is to be collected, said molten iron containingsoluble carbon oxygen, subjecting said stream of molten iron to a vacuumequivalent to a pressure of less than about 1/10 of an atmosphere,impinging said stream upon a protuberance arranged in the path thereofin said receptacle to break up the said stream into molten droplets ofiron thereby reducing the ferrostatic pressure upon the molten iron ofsaid stream and increasing the exposed area of said stream to saidvacuum whereby to induce the formation of gaseous oxides of carbon fromsaid soluble carbon and oxygen of said stream and continuing theapplication of said vacuum to remove said gaseous oxides from saidstream and reduce the carbon content of the molten iron collected insaid receptacle to an amount below 0.03% by weight and introducing solidaluminum into said receptacle in a manner that the aluminum is broughtinto contact with tbe substantially degassed stream of molten dropletsof iron beneath the same, and aluminum being in amount to make a ductileiron-aluminum alloy containing about 3 to 12% by weight of aluminum.

4. The process of preparing ductile iron-aluminum allows comprisingdirecting a stream of molten iron having a carbon content above about0.03% and up to about 0.2% by weight from a source thereof to a point ofcollection, said molten iron containing soluble carbon and suflicientsoluble oxygen to combine as gaseous oxides of carbon with substantiallyall of said soluble carbon, inducing the formation of said gaseousoxides of carbon by subjecting said stream of molten iron to a vacuumequivlanet to a pressure of less than about 1,510 of an atmosphere, andafter subjecting said stream to said vacuum forcibly disintegrating saidstream to one of droplets of molten iron to increase the area of saidstream exposed to said vacuum, continuing the application of said vacuumto remove said gaseous oxides of carbon from said stream and to reducethe carbon content of said molten iron at said point of collection to anamount below 0.03% by weight and introducing solid aluminum into saidmolten iron at the point of collection in a manner that the aluminum isbrought into contact with the substantially degassed stream of dropletsof iron beneath the same, said aluminum being in amount to produce aductile iron-aluminum alloy containing between 3 to 12% by weight ofaluminum.

5. The process of preparing ductile iron-aluminum alloys comprisingmelting by induction heating a charge of iron having a carbon contentabove 0.2% and up to about 1% by Weight and containing soluble carbonand oxygen to combine with the soluble carbon subjecting said charge toa vacuum equivalent to a pressure of less than about 1A@ of anatmosphere while agitating the same by induction to evolve gaseousoxides of carbon from the soluble carbon and the oxygen of said melt,then directing a stream of said melt to a point of collection whilestill subjecting said stream to vacuum and prior to reaching said pointof collection and while still subject to the action of said vacuumforcibly acting upon said stream to disperse said stream into dropletsof molten iron whereby to induce the formation of further gaseous oxidesof carbon from further soluble carbon and the oxygen in said stream ofdroplets and to effect removal of said gaseous oxides of carbontherefrom whereby the carbon content of said molten iron at said pointof collection is below 0.03% by weight and introducing solid aluminuminto said molten iron at the point of collection in a manner that thealuminum is brought into contact with the substantially degassed streamof droplets of iron beneath the same, said aluminum being in amount toproduce a ductile iron-aluminum alloy con` taining between about 3 to12% by weight of aluminum.

6. The process of preparing ductile iron-aluminum alloys comprisingsubjecting a mass of iron having a carbon content above 0.2% and up toabout 1% by weight and containing soluble carbon and suicient oxygen tocombine with the soluble carbon to melting under a protective blanket ata temperature sufficiently high to effect a reaction between the solublecarbon and the oxygen and the evolution of gaseous oxides of carbon fromthe melt, then directing a moving stream of the molten iron as thustreated into a collection receptacle and during said movement forciblydispersing said stream into droplets of molten iron and subjecting saiddispersed stream to a vacuum corresponding to a pressure less than about1/10 of an atmosphere whereby to reduce the carbon content of the molteniron in said receptacle to below 0.03% by weight and introducing solidaluminum into the molten iron at the point of collection in a mannerthat the aluminum is brought into contact with the substantiallydegassed stream of droplets of iron beneath the same, said aluminumbeing in amount to produce a ductile iron-aluminum alloy containingbetween about 3 to 12% by weight of aluminum.

7. The process as claimed in claim 6, including lancing the iron meltwith oxygen while under said protective blanket.

8. The process of making ductile iron-aluminum alloys comprisingdirecting a stream of molten iron having a carbon content above about0.03% `and up to about 0.2% by weight from a source thereof to areceptacle in which said molten iron is to be collected, said molteniron containing soluble carbon and oxygen, delivering to said receptacleprior to receiving said molten iron a quantity of aluminum in solid formin amount to produce an iron-aluminum alloy having between about 3% to12% by weight of aluminum, mixing said solid aluminum with said molteniron to melt said aluminum and distribute the same through said iron,and prior to mixing said aluminum with said molten iron dispersing saidstream to produce a stream of droplets of molten iron and subjectingsaid dispersed stream to a vacuum equivalent to a pressure of less thanabout 1%() of an atmosphere whereby to induce the formation of gaseousoxides of carbon from the soluble carbon and oxygen of said stream andits removal therefrom.

9. The process as claimed in claim 8 wherein the aluminum is in wireform and is fed into the dispersed stream of molten iron at the basethereof at a substantially constant rate in accordance with the rate offlow of the molten iron to said receptacle.

10. The process as in claim 8 wherein the aluminum is in the form ofpellets which are fed into the dispersed stream of molten iron at thebase thereof at a substantially constant rate in accordance with therate of ow of the molten iron to said receptacle.

11. The process as claimed in claim 1 wherein said aluminum is in amountto produce an alloy having between 31/2% to 8% by weight of aluminum.

12. The process as claimed in claim 5 Where there is an excess of oxygenin the melt.

13. The process as claimed in claim S where there is suicient oxygen inthe melt to combine with the soluble carbon and part of the oxygen issupplied by lancing the melt therewith.

14. The process as claimed in claim 6 where the oxygen is sucient tocombine with the soluble carbon and a part of the oxygen is present assoluble oxygen and part as an oxide.

References Cited by the Examiner UNITED STATES PATENTS 1,277,523 9/1918Yensen 75-49 2,253,421 8/1941 De Mare 75-49 2,259,342 10/ 1941 Harder75-129 2,726,952 12/1955 Morgan 75-49 2,776,204 1/1957 Moore 75-492,788,270 4/ 1957 Nisbet 75-49 2,930,690 3/1960 Meinen 75-129 2,993,7807/ 1961 Allard 75-49 2,994,602 8/ 1961 Matsuda 75-49 3,145,095 8/ 1964Franzen 75-49 FOREIGN PATENTS 613,169 1/1961 Canada.

338,409 11/1930 Great Britain. 35-15205 10/ 1960 Japan.

OTHER REFERENCES N. A. Ziegler: Gases Extracted From Iron-Carbon Alloysfor Vacuum Melting, AIMME Transactions (Iron and Steel Diifusion),published by the Institute, New York, 1929, pages 428-445.

DAVID L. RECK, Primary Examiner.

1. THE PROCESS OF PREPARING DUCTILE IRON-ALUMINUM ALLOYS COMPRISINGDIRECTING A STREAM OF MOLTEN IRON HAVING A CARBON CONTENT ABOVE ABOUT0.03% AND UP TO ABOUT 0.2% BY WEIGHT FROM A SOURCE THEREOF TO ARECEPTACLE IN WHICH SAID MOLTEN IRON IS TO BE COLLECTED, SAID MOLTENIRON CONTAINING SOLUBLE CARBON AND OXYGEN, SUBJECTING SAID STREAM OFMOLTEN IRON TO A VACUUM EQUIVALENT TO A PRESSURE OF LESS THAN ABOUT 1/10OF AN ATMOSPHERE AND DISPERSING SAID STREAM WHILE SUBJECT TO SAID VACUUMTO REDUCE THE FERROSTATIC PRESSURE THEREON AND PRODUCE A STREAM OFDROPLETS OF MOLTEN IRON INCREASING THE EXPOSED AREA OF SAID STREAM TOSAID VACUUM TO THEREBY INDUCE THE FORMATION OF GASEOUS OXIDES OF CARBONFROM SAID SOLUBLE CARBON AND OXYGEN IN SAID STREAM, CONTINUING THEAPPLICATION OF SAID VACUUM TO REMOVE SAID GASEOUS OXIDES FROM SAIDSTREAM AND REDUCE THE CARBON CONTENT OF THE MOLTEN IRON COLLECTED INSAID RECEPTACLE TO AN AMOUNT BELOW 0.03% BY WEIGHT, INTRODUCING SOLIDALUMINUM INTO THE RECEPTACLE IN A MANNER SUCH THAT THE ALUMINUM ISBROUGHT INTO CONTACT WITH THE SUBSTANTIALLY DEGASSED STREAM OF MOLTENIRON BENEATH THE SAME, AND INTRODUCING SAID ALUMINUM IN AMOUNT TOPRODUCE AN IRON-ALUMINUM ALLOY CONTAINING BETWEEN ABOUT 3 TO 12% BYWEIGHT OF ALUMINUM, SAID ALLOY BEING DUCTILE.